Meridian Lossless Packing
Meridian Lossless Packing, also known as Packed PCM (PPCM),Template:Citation needed is a lossless compression technique for PCM audio data developed by Meridian Audio, Ltd. MLP is the standard lossless compression method for DVD-Audio content<ref>{{#invoke:citation/CS1|citation |CitationClass=web }}</ref> (often advertised with the Advanced Resolution logo) and typically provides about 1.5:1 compression on most music material. All DVD-Audio players are equipped with MLP decoding,<ref>Template:Cite press release</ref> while its use on the discs themselves is at their producers' discretion.
Dolby TrueHD, used in Archival Disc Blu-ray and HD DVD, employs the MLP codec, but compared with DVD-Audio, adds higher bit rates, 32 full-range channels, extensive metadata, and custom speaker placements (as specified by SMPTE).<ref name="DolbyLabsDescription"> Dolby Laboratories. "Dolby TrueHD (MLP) high-level bitstream description". 2018 p. 6. </ref>
Standard DVD has a maximum transfer rate of 9.6 Mbit/s, around 70 percent of the bit rate needed to store 6 uncompressed audio channels of 24-bit/96 kHz. Should MLP not be able to compress the stream below the maximum transfer rate – or in case there is a need to reduce the size to fit overall disc capacity – it can exploit (lossy) pre-quantification zeroing out least significant bits when necessary.<ref> Meridian Lossless Packing (MLP) in a Nutshell. </ref><ref> "MLP Lossless Compression" by Bob Stuart of Meridian Audio, Ltd. </ref><ref>"A Proposal for the High-Quality Audio Application of High-Density CD Carriers" proposal by Bob Stuart, 1996, Table 3.</ref> The MLP stream can also contain "substreams", like surround and stereo downmix, which need not be of the same bit depth or sampling frequency – this further enables (lossy) pre-processing to save space. TrueHD streams cannot do this<ref>MLP on MultimediaWiki</ref> (likely because Blu-Ray discs have higher storage capacity).
MLP is streamable: A decoder can pick up the stream and start decoding from that point on nearly instantly, where the encoder has inserted a "restart block" in the stream.<ref>Dolby Laboratories 2018, section 2.4</ref> Typically, restart information is inserted approximately every 5 ms in the audio,<ref> Robert C. Maher. "Lossless Compression of Audio Data". p. 266.</ref> about the same as a typical 96 kHz FLAC stream.
MLP in packaged media formatsEdit
| Media format | Status | Channels | Max. bit rate |
|---|---|---|---|
| HD DVD | Mandatory | 2 to 8 | 18 Mbit/s |
| Blu-ray | Optional | 2 to 8 | 18 Mbit/s |
| DVD-Audio | Mandatory | 1 to 6 | 9.6 Mbit/s |
| DVD-Video | Not available | ||